Odpowiedź:
[tex]\frac{1}{1-sin^2\alpha}=tg^2\alpha + 1[/tex]
[tex]1 = (1-sin^2\alpha)(tg^2\alpha + 1)[/tex]
[tex]1 = \left(1-sin^2\alpha\right)\left(\frac{sin^2\alpha}{cos^2\alpha}+1\right)[/tex]
[tex]1 = cos^2\alpha \left(\frac{cos^2\alpha + sin^2\alpha}{cos^2\alpha}\right)[/tex]
[tex]1 = cos^2\alpha + sin^2\alpha[/tex]
[tex]L = P[/tex]
c.k.d.
